older extenders, what to do?

I have Canon 2X (original edition) and 1.4X (II edition) extenders. I use them mainly with my 70-200L f/4 IS. I am now using them on full frame, after selling my 7d to get a 5d3.

I don't know whether to keep them, replace them with the III editions, or sell them and hope to buy either a 400L 5.6 II with IS or a 300L F/4 II IS + a 1.4X III extender, if Canon ever gets around to releasing either one of these II edition lenses.

How much difference is there between these and the III edition of each?

Thanks for any expertise on this.
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Peter